Over recent years, due to simple and inexpensive production of images, an ink-jet recording system has been used in a wide variety of printing fields including specialty printing such as photograph, various types of printing, marking, and color filters. Generally, a water-based ink-jet ink containing water as a main solvent is recorded onto exclusive paper with ink absorbability serving as a recording medium. There have also been put into practical use ink-jet systems, other than such a water-based one, such as a phase-change ink-jet system utilizing wax ink which is solid at room temperature; a solvent-based ink-jet system utilizing ink mainly containing a quick-drying organic solvent; and an actinic radiation curable-type ink-jet system carrying out cross-linking via irradiation of actinic energy beams (radiation) such as ultraviolet radiation (UV light) after recording.
Of these, over recent years, attention is being paid to the ultraviolet radiation curable-type ink-jet system in view of emission of a relatively low odor, quick-drying properties, and printability onto recording media with no ink absorbability, compared to the solvent-based ink-jet system. Accordingly, a wide variety of actinic radiation curable-type ink-jet technologies have been disclosed.
Actinic radiation curable-type ink-jet inks employing radically polymerizable compounds represented by (meth)acrylates have been put into practical use. Due to adhesion to recording media, less odor, and less polymerization inhibition by oxygen, actinic radiation curable-type ink-jet inks employing cationically polymerizable compounds, as well as ink-jet printers utilizing the same have recently been proposed (for example, refer to Patent Documents 1, 2, and 3).
In contrast, as to an ink-jet head, there is frequently used a metal such as stainless steel or aluminum as a material constituting an ink supply path in the head and a filter to remove foreign substances.
In a water-based ink-jet head commonly used, a metal inside the head was often corroded by water present in an ink. Such corrosion often caused clogging by corroded materials in the ink-jet head, whereby, in severe cases, the ink-jet head itself was frequently disabled completely. Therefore, to prevent contact of the metal surface with water, a resin has been coated on the liquid contact portion of the metal (for example, refer to Patent Document 4).
On the other hand, when ink ejection for recording is carried out using an ink containing a photopolymerizable compound from an ink-jet head constituted of the metallic material as described above, despite almost no corrosion of the metal constituting a liquid contact portion of the ink-jet head due to almost no presence of water in the ink, precipitates have become confirmed inside the ink-jet head with the elapsed time of ejection of the ink-jet ink. It has been found that these precipitates caused clogging of the ink supply path, and then reaching thereof to the nozzle section caused ejection failure.
In general, precipitation with respect to an actinic radiation curable-type ink-jet ink is caused by leaked light of actinic radiation or pigment aggregation in some cases, and therefore various countermeasures against these phenomena have been taken so far. However, with regard to a cationically polymerizable ink, when a metallic material was used as a liquid contact member of an ink-jet printer, it has been found that undesirable electrochemical reaction occurred and thereby decomposed materials or polymerized materials of ink components were generated. When a metallic material is used as the liquid contact member of an ink-jet printer in this manner, unexpected ink polymerization reaction has been found to occur with long-term contact of a cationically polymerizable ink with the metallic material.
Such a metallic material is commonly, for example, an electrically conductive material. For example, SUS, copper, or aluminum is employed as a conductive liquid contact member in an ink flow path of an ink-jet printer. Further, an example is known in which a conductive liquid contact member is employed for an ink-jet head of an ink-jet printer. It is thought that these electrically conductive members usually exhibit excellent durability to various inks such as a water-based ink-jet ink, a solvent-based ink-jet ink, an oil-based ink-jet ink, an ultraviolet radiation curable-type ink-jet ink, and a solid-based ink-jet ink; and also adversely affect such inks only to a small extent.
It was found that when any of these electrically conductive members came into contact with a polymerizable, conductive ink, undesirable electrochemical reaction occurred, whereby decomposed materials or polymerized materials of ink components were generated in a flow path or an ink-jet head. Further, corrosion causes metal dissolution. Accordingly, when an ink containing a polymerizable compound is used, this electromotive force or metal dissolution triggers unexpected ink polymerization reaction in cases when the ink remains in contact with the interior of the flow path or ink-jet head over a long-term period. Especially, a cationically polymerizable actinic radiation curable-type ink-jet ink containing a photolytically acid generating agent such as an onium salt as an essential material tends to produce such a problem due to relatively high electrical conductivity of the ink.
These reaction products are not redissolved in the ink. Therefore, deposition thereof in an ink-jet head, specifically in a nozzle peripheral portion causes a decrease in ejection straightness. In worst cases, unrecoverable nozzle clogging is caused.    Patent Document 1: Unexamined Japanese Patent Application Publication No. (hereinafter also referred to as JP-A) 2005-290246    Patent Document 2: JP-A 2004-34543    Patent Document 3: JP-A 2005-238742    Patent Document 4: JP-A 2006-159619